The present invention relates to liquid ejection apparatuses such as inkjet printers and cleaning methods for liquid ejection apparatuses.
As a liquid ejection apparatus that ejects liquid from a liquid ejection head to a target, an inkjet recording apparatus (hereinafter, a “printer”), for example, is known. The printer includes an ink cartridge (a liquid retainer) and a recording head (a liquid ejection head) mounted on a carriage. The ink cartridge retains ink (liquid) and supplies the ink to the recording head. Normally, the printer includes a pressurization pump (a pressurization device) that sends pressurized air to the ink cartridge. This pressurizes the ink retained in an ink pack accommodated in the ink cartridge and thus sends the ink to the recording head. The ink is then ejected onto a recording medium (a target) through a nozzle of the recording head, thus subjecting the medium to printing (see, for example, Japanese Laid-Open Patent Publication No. 2000-352379).
The recording head has a piezoelectric element as well as the nozzle. When the piezoelectric element is actuated, the ink is introduced into the nozzle and then ejected from an opening defined in the nozzle. The solvent of the ink thus may easily evaporate from the opening of the nozzle. Further, the viscosity of the ink may be increased in the nozzle and thus clog the nozzle. Also, the atmospheric air may enter the nozzle from the nozzle opening and mix with the ink, generating bubbles in the ink. The bubbles may cause a printing problem such as a missing dot. To avoid these problems, printer cleaning methods including choke cleaning methods or selective cleaning methods have been known (see, for example, Japanese Laid-Open Patent Publication No. 2004-90453).
In choke cleaning, a valve (an open-close valve) located upstream from the recording head is closed. A nozzle surface of the recording head is then subjected to suction by a suction pump (a suction device), generating negative pressure in the recording head. The bubbles in the recording head are thus expanded. Subsequently, the valve (the open-close valve) is opened and allows the ink to rapidly flow into the recording head. The ink having the increased viscosity and the expanded bubbles are thus drained from the nozzle, or the recording head.
The pressurization pump of Japanese Laid-Open Patent Publication No. 2000-352379 may be connected to the ink cartridge of Japanese Laid-Open Patent Publication No. 2004-90453. If the choke cleaning is performed on this printer, the valve is normally opened through pressurization by the pressurization pump. Since the pressurization pump is formed by a diaphragm type that pressurizes the valve in accordance with each stroke, the pressure in the ink cartridge increases in a stepped manner. Further, the amount of the ink consumed in each cycle of the choke cleaning cycle is normally measured as being the same as a fixed basic value, which corresponds to the amount of the ink consumed in a single choke cleaning cycle performed when the ink pack is full.
However, if the amount of the ink remaining in the ink pack decreases, the volume of the air retained in the ink cartridge correspondingly increases. The efficiency of pressurization by the pressurization pump in accordance with the stroke movement of the pressurization pump is thus lowered. This prolongs the time for raising the pressure of the pressurization pump to a level sufficiently high for opening the valve, and thus decreases the (actual) drainage amount of the ink. In other words, since the actuation time of the pressurization pump is constant, the time for drawing (draining) the ink is shortened if the prolonged time is necessary for sufficiently raising the pressure of the pressurization pump.
As a result, as the ink remaining amount of the ink pack becomes smaller, the difference between the actual ink consumption amount of the choke cleaning and the value determined in correspondence with the fixed basic value becomes greater. The ink thus unnecessarily remains unused, or is wasted, by an amount corresponding to the difference.